We have developed a generalization of the Zeldovich approximation that is exact in a wide variety of situations, including planar, spherical, and cylindrical symmetries. We have shown that this generalization, which we call the complete Zeldovich approximation (CZA), is exact to second order at an arbitrary point within any field. For Gaussian

The case of the possible 11 yr periodicity in the historical light curve of OJ 287 over a century of observations is examined critically largely independently of possible models that may explain it. Although it is evident that there is at least a quasiperiodicity in the light curve because of the regular spacing of the nine observed outbursts

We present results of the inversion of spatially averaged Stokes I and V profiles emerging from plage regions near disk center. The observations analyzed in this work were recorded with the Advanced Stokes Polarimeter. All atmospheric quantities determining the radiative transfer in the thin flux-tube approximation are inferred self-consistently

We present a study of the H II regions in the central area of the giant irregular galaxy NGC 4449 based on observations taken on the William Herschel Telescope at the Roque de los Muchachos observatory with the Taurus II Fabry-Perot interferometer in the emission lines of Hα and [O III] 5006.8. We show that the usual methods of determining sizes of

We present the first part of the first large and homogeneous CCD color-magnitude diagram (CMD) data base, comprising 52 nearby Galactic globular clusters (GGC) imaged in the V and I bands using only two telescopes (one for each hemisphere). The observed clusters represent 75% of the known Galactic globulars with (m-M)_V

We compute photoionization models for the giant extragalactic H II region NGC 2363, and compare them with optical observational data. We show that models computed with the observed metallicity of the cluster (Z=0.10 Zodot) do not reproduce the observed features of the spectrum, and that the disagreement can be overcome by allowing for spatial